Embodiments of the present embodiments described herein generally relate to implantable medical devices, and more particularly to antennas for use therein.
An implantable medical device (“IMD”) is a medical device that is configured to be implanted within a patient anatomy and commonly employ one or more leads with electrodes that either receive or deliver voltage, current or other electromagnetic pulses (generally “energy”) from or to an organ or tissue for diagnostic or therapeutic purposes. In general, IMDs include a battery, electronic circuitry, such as a pulse generator and/or a processor module, that are hermetically sealed within a metal housing (generally referred to as the “can”), and a microprocessor that is configured to handle radio frequency (RF) communication with an external device, as well as control patient therapy.
IMDs are programmed and monitored by an external programmer or external home-based patient care system. RF circuitry and an antenna are embedded within the housing of the IMD, such as the header or adjacent to the header, to allow data communication with the external device or base system. In the past, the IMD was configured to communicate bi-directionally with the external programmer or base system using the Medical Implant Communication Service (“MICS”) specification. The MICS specification is defined under 47 C.F.R. 95.601-95.673 Subpart E (incorporated herein by reference) and ETSI EN 301 839-1 (incorporated herein by reference). The MICS protocol uses a frequency band between 402-405 MHz and a transmit power of approximately 25 microwatts. Problems have arisen in designing the antenna for use in the IMDs. In particular, there can be a loss of RF communication performance due to the reduction in size of the header and the housing (also called the “can” or “case”) of the IMD. Further, attenuation is inherent to the system since the RF signal travels through the lossy human body.
Another problem is how to assemble an efficient RF antenna into a compact space such as an IMD header. It has been proposed to provide a loop or an inverted E-shaped configuration antenna mounted on the IMD. The antenna makes use of a capacitive plate at a tip in order to tune to a correct frequency of approximately 400 Mhz. Due to the frequency tuning, the capacitive plate allows a reduction in the electrical length of the antenna to enable the antenna to fit physically within the header of an IMD. While the proposed antenna works very well fbr the MICS frequency band, the proposed antenna is better suited for frequencies in the lower RF region (less than 1 GHz). With the introduction of Bluetooth Low Energy (BLE) communications in IMD, the operating frequency increases to 2.4 GHz which is a 6× increase from 400 MHz MICS communication.